Bund and Containment Area Repairs and Crack Sealing
Prior to applying any Bund lining or protective coating in a primary or secondary containment tank or area over an existing structure, it is always necessary to first inspect and where necessary then carry out repairs to any visible damage or cracks in the concrete surface. Otherwise these can be reflected through the newBund Lining and render it useless, as the liquids that are intended to be contained could penetrate and attack the structure, or escape and contaminate the area.
The idea of leaving any unsound or damaged concrete or masonry in place, followed by overlaying this with a build-up of a fibreglass system insitu that has unfortunately managed to become a ‘standard’ approach for many less technically competent contractors, is not normally an optimum solution. Covering up structural damage, che,ical attack and deteriorated concrete base slabs and walls is never a good idea and may be a huge risk and future liability for you and your company (individuals are also now held to account as being liable under the latest legislation on environmental pollution and also Health and Safety requirements. This is because the future structural integrity cannot be ensured and there is the potential for further unseen deterioration and possibly wash-out and void creation beneath the fibreglass layer.
This could obviously have pretty disastrous consequences – i.e. unforeseen structural failure, potential contamination or infestation with vermin for example. Therefore any damage or defects anywhere or in anything that is to be ‘unseen’ in the future, is always best made good and structurally sound, with any defective or damaged materials removed and properly disposed of, before any overlays or overcoating of any kind is undertaken. A fibreglass build-up system insitu / onsite is also usually the most expensive solution for a new bund lining system, so as with cheaper factory preformed GRP bund liners, these are both really only suitable for small domestic and non-critical industrial and commercial bund lining requirements.
Additionally, it is important that the precise nature and the cause of any cracks (i.e. moving or non-moving), or any damaged joints and joint arrises in the concrete, and their potential capacity for movement in the future, must also be considered and treated appropriately. This is to ensure that there will be no possibility of contamination or adverse future cracking, due to this potential movement, which could otherwise also then adversely affect the integrity of your expensive new protective bund lining system.
Concrete Repairs
Repairs can be required to make good surface damage to concrete substratesfor many different reasons, including defects in the original concreting work, i.e. honeycombing, poor compaction voids, the use of unsuitable or ‘soft’ aggregates such as ‘mudstone’ which leads to ‘pop-outs’ as they disintegrate, inadequate surface finishing or lack of correct concrete curing, etc. Damage to concrete surfaces can obviously also be caused by impact, wear and abrasion, or by chemical exposure and attack if left without a suitable protective coating or lining during service.
With all damaged concrete surfaces that are being prepared so that they are suitable to receive a new bund lining protective coating system, the first requirement is to establish the root cause and the full extent of the damage. The next stage is to mechanically break out and completely remove any unsound or weak concrete, always ensuring that any cracks and/or voids in the slab and / or any areas of honeycombing are fully exposed.
The best method of concreterepair to use on a bunded area should be selected according to the following criteria: the size and depth of concrete repairs required, the extent and function of any exposed reinforcing steel, the type of the new resin bund lining system to be installed, thefuture exposure and performance required, plus the time available and the environmental conditions at the time.
Basically soundand durable concrete surface ‘patch’ repairs can usually be made with pre-bagged cement based mortars (such as Sika MonoTop products), or epoxy resin based mortars (such as the Sikadur range). Larger, thicker areas of concrete damage are usually always repaired with pre-bagged cement based mortars or site batched modified cement mortars due to their lower cost and good application and cured mechanical properties, providing there is sufficient time for them to harden and cure to the acceptable moisture content for the resin lining system selected. However if time is short, then rapid hardening cement based products, or even faster hardening epoxy resin repair mortars can also be used, such as the Sikadur range of epoxy resin based mortar systems.
Epoxy resin repair mortars are much more expensive than those based on cement of course, but generally with epoxy repairs the new resin lining system can go ahead the very next day, thereby reducing any delays due to waiting times. With almost all cement based mortars, at least 7 days will be requiredbefore their moisture content has dropped to a level that is suitable to be over-coated with the epoxy resin lining materials.
Technically this is because of a combination of reasons – time to dry and harden, time for the mortar to reach an acceptably low moisture content, plus the time required for the mortars surface alkalinity to be neutralised (by natural atmospheric carbonation).
Another unique option for fast surface repairs is provided by the Sika EpoCem system, a combination of epoxy and cement technology that allows repairs to be made on a damp substrate but in most bund situations will also cure quickly and produce a surface that can be over-coated / overlaid with the main impermeable, chemically resistant bund lining material the next day. Where time is really critical in a project, then concrete damage can be repaired and defects filled with rapid reacting and hardening polyurea systems, such as the QuickRepair systems from VIP, which can harden and be overcoated in hours or even minutes if required.
NCC Bund Lining stock a full range of all of these concrete repair products in our Depots and supply them all around the UK, including concrete additives to improve the strength and reduce the initial water content of site-batched cement repair mortars (i.e. Sika latex and SikaCem 810), a range of different pre-batched cement and rapid hardening cement based repair mortars (i.e. SikaTop, Sika MonoTop and Fosroc’s Renderoc ranges) for different thicknesses and areas, plus a full range of epoxy resin based concreterepair products (i.e. Sikadur systems), and the advanced Sika EpoCem systems for damp concrete and the VIP QuickRepair and VIP QuickPrime systems for really fast application and curing requirements.
If there are additional structural implications then NCC can also supply and advise on the use and installation of resin anchors for new steel reinforcing bars (i.e. Sika Anchorfix-1 or Sika Anchorfix-2), plus the selection and use of composite structural strengthening systems using carbon fibre and / or aramid based plates or fabrics according to the structural demands – such as the Sika CarboDur and SikaWrap range of systems.
Therefore whatever damage has happened on your concrete we can provide detailed repair recommendations and method statements, together with all of the necessary materials required and our onsite repair works support and even supervision as necessary.
For advice and assistance in any aspect of concrete repairs or strengthening of bunds and primary or secondary containment facilities, please call any of our offices and one of ourspecialists will be pleased to assist you.
Crack Repairs
Cracks in concrete can be caused by a number of individual construction problems, or a combination of different reasons during the construction including concrete shrinkage or inadequate provision for joints; or post construction due to building movement or settlement, vibration, excessive loading or impact.
To successfully repair cracks in concrete and effectively seal the cracks for the future, it is important to understand the exact reason for the crack and also if any further crack movement will occur. This is obviously a technical issue and so a qualified Structural Engineer should normally be involved to correctly determine this. Correct diagnosis of the reasons for and the nature of any cracks in the concrete and masonry structures, is also essential during new bund and containment tank construction projects, it is always important to do this as early as possible, in order to determine the correct remedial action.
The specialists at NCC Bund Lining can advise you on how best to investigate, evaluate and repair any cracks in your concrete bund and containment areas. There is more detailed information below or if you are uncertain how to proceed with cracks that are evident on your project, then please call any of our offices and one of our specialists will be pleased to assist you.
Repairing Moving Cracks and Sealing Joints in Concrete
If the cracks in the structure are still likely to be subject to future movement – for example due to thermal exposure or variable loadings etc., then unless a highly elastic lining system is used and one that can fully accommodate the level of movement anticipated by the Structural Engineer(which can often be difficult to determine in existing structures), then these cracks should be treated as Movement Joints - see below - Basically they should be cut square to the concrete surface, brought through the protective resin bund lining finish, and sealed with an appropriate chemically resistant joint sealant, such as Sikaflex PRO 3WP horizontally and Sikaflex-Pro-2HP vertically, or by use of the highly chemically resistant Sikadur Combiflex SG system for over-banding variable movement joints and cracks.
The Sikadur Combiflex SG system can safely seal and accommodate substantial movement in wide or irregularly dimensioned joints and cracks, plus it is also an excellent solution when the crack or joint is itself contaminated with a failed exisiting sealant or other material, such as bitumen or silicone that cannot effectively be removed. This unique system is also approved for use in contact with potable water by the DWI and so it is also suitable for use repairing and sealing this type of joint and cracks in drinking water storage tanks and reservoirs.
Repairing Non-Moving Cracks and Construction Joints in Concrete
If the Structural Engineers’ assessment is that a crack is no longer moving, then it can be more simply repaired by cutting out the damaged and unsound material, then filling and sealing it with a suitable cement or resin based repair mortar, prior to applying the new protective bund lining system. The best procedure and materials for doing this repair is dependent on the width, depth and length of the crack, and this same procedure also applies to non-moving and bonded construction joints in the original concrete structure. It is likely that the surface of cracks or construction joints will need opening / cutting out to remove any loose materials and then it can be either ‘surface sealed’ with a fine epoxy mortar, such as Sikadur 31. This is pressed firmly into the surface to fill and seal the cracks with a small trowel. Alternatively where preferred by the Structural Engineer, the crack repairs can be achieved by structurally bonding them across the crack to restore full integrity and load transfer capability; this can be achieved with a low pressure epoxy resin injection product, such as Sikadur 52 Injection for example.
All of these concrete repair and crack sealingmaterials, plus detailed specifications and method statements for their installation are available from NCC Bund Lining - For detailed advice on sealing any non-moving cracks or construction joints on your specific project, please call any of our offices and one of ourspecialists will be delighted to assist you.
Concrete Movement Joints and Movement Joint Arris Repairs
Concrete Movement or Expansion joints that are correctly designed, located and formed in new construction works should normally be sealed with an appropriately chemically resistant joint sealant with the correct movement capability, after the new protective resin bund lining has been installed.
Existing movement joints in existing concrete structures should be brought through the new protective resin bund lining system and also sealed with an appropriately chemically resistant joint sealant with the correct movement capability, after the new protective resin bund lining has been installed. However, dependent on the nature of any deteriorated existing sealant, there may be some such as existing bitumen, polysulphide or silicone joint sealants, which cannot easily be removed or over-coated with resinbased bund lining materials. These will therefore either need to be completely removed with substantial time, effort and cost, or they can alternatively be sealed using a chemically resistant, elastic over-banding jointing solution such as the Sikadur Combiflex SG system.
If the joint arrises are broken and damaged, then these should be cut out and repaired prior to applying the new resin bund lining and then the new joint sealant. High strength epoxy resin mortars are usually the best materials for durable joint arris repairsthat are to be exposed to any abrasion or traffic, because of the high dynamic loads that this can impose on the joint edges. The best type of replacement joint sealant is also dependent on the type of material that was used for the failed existing joint sealant, i.e. different joint sealant types can be incompatible with the same or different joint sealing materials, which means that they will not bond with previous sealant residue on the joint sides. This is a particular problem with old bituminous sealants in the joints that will almost always require specialist removal and treatment, or use of the Sikadur Combiflex SG system, for long term durability of the new bund lining and its joint sealing system.
NCC Bund Lining supply a full range of epoxy resin mortars that are ideally suited to repair this sort of damaged joint arrises, together with a full range of chemically resistant, elastic joint sealants, based on all of the available joint sealing material types, including the very versatile Sikaflex range of high performance, easily applied, chemically resistant, elastic, single pack, gun or flow applied, polyurethane resin based joint sealants, which aregreat for solving a great many bund and containment area jointing requirements. The Sikadur Combiflex SG system is also a permanent stock item in all NCC Depots, due to its tremendous problem solving capabilities for so many difficult jointing and sealing situations.
For specific advice for repairing or sealing the joints on your specific project please call any of our offices and one of our specialists will be pleased to assist you.
Photographs can often help to identify the correct procedure and products to use for remedial works such as concrete repairs, crack sealing and joint arris repairs. These can be sent to technical@nccinaction.co.uk for the attention of David or Gary, and we will get right back to you with a proposal and solution for your project requirements just as soon as possible.